Plasma processing has been widely used in the semiconductor and other industries for many decades. Plasma processing is used for tasks such as cleaning, etching, milling, and deposition. In many plasma processing systems, charge tends to accumulate on the substrate being processed. This charge build-up can result in the development of a relatively high potential voltage on the substrate that can cause plasma processing non-uniformities, arcing, and substrate damage. For example, charge build-up in plasma etching systems can result in non-uniform etch depths and pitting or damage to the surface of the substrate which can reduce process yield. In addition, charge build-up in deposition system can result in non-uniform deposition and damage to the deposited film layer.
More recently, plasma processing has been used for doping. Plasma doping is sometimes referred to as PLAD or plasma immersion ion implantation (PIII). Plasma doping systems have been developed to meet the doping requirements of some modern electronic and optical devices. Plasma doping is fundamentally different from conventional beam-line ion implantation systems that accelerate ions with an electric field and then filter the ions according to their mass-to-charge ratio to select the desired ions for implantation. In contrast, plasma doping systems immerse the target in a plasma containing dopant ions and bias the target with a series of negative voltage pulses. The electric field within the plasma sheath accelerates ions toward the target thereby implanting the ions into the surface of the target.
Plasma doping systems for the semiconductor industry generally require a very high degree of process control. Conventional beam-line ion implantation systems that are widely used in the semiconductor industry have excellent process control and also excellent run-to-run uniformity. Conventional beam-line ion implantation systems provide highly uniform doping across the entire surface of state-of-the-art semiconductor substrates.
In general, the process control of plasma doping systems is not as good as conventional beam-line ion implantation systems. In many plasma doping systems, charge tends to accumulate on the substrate being plasma doped. This charge build-up can result in the development of a relatively high potential voltage on the substrate that can cause unacceptable doping non-uniformities and arcing, which can result in device damage.